The unit files have no [Install] section. They are not meant to be enabledusing systemctl.Possible reasons for having this kind of units are:1) A unit may be statically enabled by being symlinked from another unit's .wants/ or .requires/ directory.2) A unit's purpose may be to act as a helper for some other unit which has a requirement dependency on it.3) A unit may be started when needed via activation (socket, path, timer, D-Bus, udev, scripted systemctl call, ...).